1. Technical Field
This invention relates generally to vibration damping means and more particularly to an active vibration damping system for damping the structural appendage vibrations of a spacecraft.
2. Background Art
One type of conventional spacecraft comprises a space platform which typically includes a rigid resource module, a relatively flexible truss like instrument section, and one or more deployable solar arrays. The instrument section and solar arrays are relatively long and flexible, having lengths, for example, from 45 to 60 feet. These elongated structural appendage elements have a tendency to flex when subjected to thermal disturbances when moving in and out of the earth's shadow, during slewing attitude control maneuvers and as a result of internal disturbances caused by the moving parts within the instrument section itself. These disturbances induce structural vibrations which persist for relatively long lengths of time because of the normally small inherent structural damping of the spacecraft. The persistent vibrations can degrade the scientific and engineering missions of the space platform
It should be noted that zero momentum, non-spinning, 3 axis controlled space platforms, to which this invention is applicable, normally carry a propulsion subsystem and an attitude control subsystem in the rigid resource module. Linear accelerometers comprise an element of the propulsion system and rate gyros comprise an element of the attitude control system (angular acceleration can be obtained by differentiation of the rate gyro information). These elements are utilized in the subject invention as well as other components that are placed at the appendage tips as will be disclosed hereinafter.
Current state of the art spacecraft structural damping systems use either passive or active damping techniques. Passive damping apparatus is relatively simple but has the inherent limitation of being excessively heavy and requires an undesired long duration of time to dampen motion, particularly low frequency vibrations. Active methods typically employ several sensors and actuators which are distributed within the structure. This necessitates complicated signal processing requiring the use of a relatively powerful computer, resulting in a relatively heavy, bulky package which causes significant electrical power drain.